fix initialization of counter

src/counter.js

@@ -1,6 +1,8 @@
 class Counter {
-  constructor(redis) {
+  constructor(redis, name) {
     this.redis = redis
+    /* assume the key is called "clicks" */
+    this.name = name == undefined ? "clicks" : name
     /* make sure we don't miss errors */
     this.redis.on("error", (err) => { console.log("Error: " + err) })
   }
@@ -9,11 +11,13 @@ class Counter {
     /* default to incrementing by one */
     val = val == undefined ? 1 : val
     /* increment */
-		this.redis.incr('default')
+		this.redis.incr(this.name)
   }
   
   async state () {
-    return await this.redis.get('default')
+    let count = await this.redis.get(this.name)
+    /* keys in redis are set to null by default */
+    return count == null ? 0 : count
   }
 }